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A. Dmitri Mendeleev
Dmitri Mendeleev (1869, Russian)
• Organized elements by
increasing atomic mass.
• Predicted the existence of
undiscovered elements.
B. Henry Mosely
Henry Mosely (1913, British)
• Organized elements by
increasing atomic number.
• Fixed problems in Mendeleev’s
arrangement.
B. Table Sections
1
2
3
4
5
6
7
Lanthanides - part of period 6
Actinides - part of period 7
Overall Configuration
Periodic Law
• Properties of elements repeat
periodically when the elements are
arranged by increasing atomic
number.
A. Terms
A. Terms
Valence Electrons
• e- in the outermost energy level Atomic Radius
First Ionization Energy
• energy required to remove an e- from a neutral atom
B. Periodic Trends Group # = # of valence e- (except He)
• Families have similar reactivity. Period # = # of energy levels
1A
2A 3A 4A 5A 6A 7A
8A